Ocular aberrations typically produce unwanted results in the form of bad eyesight. To be adequately treatable, these aberrations need to be measured and characterized. To this end, various devices, apparatuses, and methods have been developed for objectively measuring characteristics, including aberrations, of a subject's eye.
During vision measurements, however, sometimes a subject will stare into the optical measurement apparatus for an unusually long period of time without blinking. When this happens, some individuals will experience a disruption of the tear film on their eye(s). The tear film consists of three layers: (1) an outer lipid layer that inhibits evaporation; (2) an inner aqueous layer; and (3) a mucin layer that lies on the cornea. The cornea repels water, so it is the function of the mucin layer to coat the cornea, and to provide a hydrophilic layer for the aqueous layer to be spread over evenly. In particular, if a subject holds her/his eye open for too long without blinking, the mucin layer may become disrupted. If that happens, it may take several minutes for the mucin layer to recoat the entire cornea. Until that happens, measurements of the eye made during the intervening period will not reflect the eye's normal optical performance. More specifically, if the corneal topography and/or refraction of the eye are measured under such a condition when the tear film layer has been disrupted, the measurement will include errors.